The present invention relates to a method for measuring the camouflaging capacity of a smoke, especially within the infra-red (IR) range, but also within the ultraviolet, the visual and the mm wave range.
During target seeking, especially for military purposes, use is often made of a target seeking camera, i.e. a camera which detects the radiation emitted from any object. One method for protecting such objects from being detected by such target seekers is hence to surround the object by a smoke which to a greater or lesser extent attenuates or absorbs the radiation from the object.
During the development of suitable smokes it has hitherto proved difficult to measure reliably the capacity of the smoke produced for camouflaging radiation. The conventional method for measurement is as follows regarding IR smoke.
After a suitable, known IR radiation source has been selected, an IR camera is aimed against the radiation source before the smoke is released. Measurements are then made of the radiation temperature t.sub.1 of the radiation received from the IR radiation source. With the IR camera still directed against the IR radiation source, IR smoke is then released between the radiation source and the IR camera. Measurements are now made of lower radiation temperature t.sub.2 on the part of the radiation from the IR radiation source. The difference t.sub.1 -t.sub.2 corresponds to the attenuation of the radiation received from the radiation source.
However the difference t.sub.1 -t.sub.2 provides no information as regards the degree to which the radiation source can, after smoke has been released, be differentiated with respect to the surroundings of the radiation source, because it provides no information as to the radiation temperature on the part of the surroundings. Hence the method does not provide any unequivocal measure of the camouflage capacity of the smoke.
The known method is particularly unsuitable when it is a question of comparing different types of smoke. A pyrotechnic aerosol, which is hot, and which thus itself emits IR radiation, gives a high background temperature which means that it becomes difficult to distinguish the radiation source, so that the smoke is deemed to have good camouflage capacity. A measurement of the said difference t.sub.1 -t.sub.2 can on the other hand indicate that the smoke gives low attenuation and hence that it would have poor camouflage capacity.
Corresponding disadvantage is present when measuring camouflaging smoke within the ultraviolet, the visual and the mm wave range.
Consequently the aim of the present invention is to provide a method of measuring the camouflaging capacity of smoke by means of which consideration is given on the one hand to the intensity of the background radiation and secondly a comparison can be made between the camouflaging capacity of hot (i.e. intensive radiating) or cold (i.e. weak radiating) smoke. This aim is achieved in that the method in accordance with the present invention is given the characteristics specified in claim 1. Further developments of the invention are described in the subclaims.